Patent GB-568543-A (GB)
Title: Improvements relating to insulating material and the like
IPC: C08J9/33
Filed: 1943-06-01
Abstract: A material suitable for heat insulation comprises cellular particles of regenerated cellulose or of a partially saponified organic ester of cellulose united by means of a binding agent into a coherent mass. The regenerated cellulose may be obtained from cellular material of cellulose esters by saponification.  A cellulose ester solution containing solid particles capable of yielding a gas may be set and the mass treated to decompose the gas-generating solid with formation of hollow spaces throughout the mass.  A cellulose ester solution containing a soluble inorganic salt in suspension may be solidified by evaporation of the solvent, and the soluble salt may then be extracted with water so as to leave a cellular mass or structure of cellulose ester.  A cellulose ester may be caused to absorb a liquid having a solvent, swelling, or softening effect and may then be subjected to an elevated temperature and to an elevated pressure which is suddenly released so as to permit rapid vaporisation of the liquid and expansion of the cellulose ester into a strong, firm, cellular material of low density and even texture.  The cellular cellulose ester material is reduced to particle form and saponified. The cellular regenerated cellulose particles are bonded into a coherent mass by the use of a binding agent.  The binding agent may be glue such as casein glue, animal glue, or vegetable glue, or it may be a cellulose derivative, such as cellulose acetate, or a resin or gum applied with a volatile solvent in the form of a solution, or applied as a powder mixed with the regenerated cellulose and then treated with a solvent to effect a binding of the particles.  The binding agent may be inorganic, e.g. sodium silicate.  A partially polymerised thermoplastic binding agent may be employed, and after shaping the mass of regenerated cellulose particles, the binding agent may be further polymerised to form a shaped insulating material.  Phenol-aldehyde, cumarone, alkyd, or polyvinyl resins, or colophany, balsam, copaiba, dammar, elemi, or mastic, may be used. The mixture of cellular particles and binding agent may be moulded to form boards or other articles.  It may be extruded through orifices by means of a screw-stuffer.  The shaped material may be treated to render it water-proof, or water-resistant, e.g. it may be coated with pitch or treated with formaldehyde.  In an example cellulose acetate is ground and mixed with butanol.  The mixture is heated to a temperature of 200 DEG  C. and pressure of 3,000 pounds per square inch gauge.  The pressure is released suddenly and the cellulose acetate is allowed to expand.  The mass is broken up into small particles and these are treated with caustic soda until the cellulose acetate is converted into regenerated cellulose.  The cellular regenerated cellulose particles are mixed with a solution of cellulose acetate and the mixture is placed in a hot square mould.  A firm cellular cake is obtained.  Fibrous fillers such as cotton, flax, hemp, ramie, jute, or silk, or other fillers such as cork, sawdust, wood shavings, clay, asbestos, or pigments, or fire-retardants such as sodium phosphate, or magnesium silicate may be incorporated in the composition.  Specification 560,940 is referred to.